1. Field of the Invention
This invention relates to methods for delivering micellular particles to tumor cells in a body. More particularly, the invention relates to methods of introducing neutral or charged phospholipid micellular particles containing chemotherapeutic agents and a marker into a patient's body to diagnose and treat such tumors.
2. Description of Prior Art
Before various abnormalities such as tumors in a patient's body can be diagnosed and treated, it is often necessary to locate the abnormalities. This is particularly true of such abnormalities as malignant tumors Since-the treatment of such tumors is often on a localized basis. For example, the location of malignant tumor cells has to be identified so that a chemotherapeutic agent can be directed to such cells to eliminate the tumor.
Various attempts have been made over an extended number of years to identify specific locations, such as tumor locations, in a patient's body by simple techniques. For example, it would be desirable for diagnostic purposes to identify the location of cancer cells in a patient's body by a simple method involving the introduction of particular mobile particles to the patient's body and the movement of such particles to the cancer cells. It would also be desirable to treat such cancer cells by introducing chemotherapeutic agents into the patient's body and having such agents move to such specific locations to combat the cancer cells at such locations. In spite of such attempts over extended periods of time, simple methods of targeting specific locations, such as tumors for diagnosis, and methods for delivering chemotherapeutic agents to the tumors in a patient's body for treatment do not exist as yet.
Placing a chemotherapeutic drug in the body orally, subcutaneously or intravenously can result in harm to the normal cells in the body which take up the drug and a worsening in the patient's condition, without achieving the desired reduction in tumor cell activity. In the past, this toxicity to normal cells in the patient's body has been a major disadvantage in the treatment of tumors with chemotherapeutic agents. The lack of efficacy of such chemotherapy is also attributable to the failure of the freely circulating drug to localize within tumor cells before it is excreted or taken up by other cells in the body.
Prior attempts to improve treatment of tumors by chemotherapeutic agents have included encapsulation of such agents within biodegradable phospholipid micellular particles in the form of vesicles or liposomes. Encapsulation is thought to reduce the potential toxicity from the circulating drugs. Researchers have also sought to utilize such encapsulation to selectively target tumors within a body for delivery of chemotherapeutics. However, until the invention disclosed in the present application and the related application Ser. No. 363,593, abandoned, such efforts to reliably place drug-encapsulating particles within tumor cells has not been demonstrated.
Because solid tumors and their metastases are located in extravascular tissues, to accomplish targeting of intravenously injected chemotherapeutic agents to the tumor cells, the agents must leave the normal circulation by crossing blood vessel membranes to enter the extra-vascular tissues. This movement is known as "extravasation". In addition the encapsulated agent must cross the tumor cell membrane. Normally, small substances such as small molecular weight proteins and membrane-soluble molecules can cross cell membranes by a process known as passive diffusion. However, passive diffusion will not allow sufficient accumulation of larger particles carrying drugs within cells to reach therapeutic levels. Additionally, cells can actively transport materials across the membrane by a process such as pinocytosis wherein extracellular particles are engulfed by the membrane and released inside the cell. Entry of encapsulating particles into individual cells may occur by pinocytosis.
Progress in targeting specific locations, such as tumor locations, with chemotherapeutic drugs encapsulated in particles such as vesicles has been hampered by the inability to achieve movement of encapsulated drug across blood vessel membranes and to detect such movement. In the usual case, large structures such as drug encapsulating vesicles cannot escape from blood vessels such as capillaries, and thus remain in the circulation. However, an examination of the structure of the vascular morphology of a tumor reveals that the various blood vessels associated with tumors, in particular capillaries, exhibit alterations in their structure as a result of tumor cell growth patterns. Studies of tumor capillary permeability suggest that these morphologic variations in the capillaries allow some substances to cross the capillary membrane. Such variations include defects in the vascular endothelium from poor cell differentiation, and breaks in vascular walls as a result of invading tumor cells. Examples of tumor-modified capillaries include vessels with interrupted endothelial lining and vessels with fenestrated endothelium. H. I. Peterson, Vascular and Extravascular Spaces in Tumors: Tumor Vascular Permeability, Chapter III, Tumor Blood Circulation, H. I. Peterson, Ed. (1979).
Notwithstanding such knowledge of tumor vascular morphology, researchers such as Peterson have concluded that transport of large molecules or materials across the tumor capillary wall occurs as a result of passive diffusion only and that "concentrations of active drugs sufficient for therapeutic effect are difficult to reach." Id. at 83.
Prior to such morphologic studies, early research on the problem of extravasation suggested that vesicles might undergo "transcapillary passage" across the capillary membranes and on into tumor cells. G. Gregoriadis, Liposomes in Biological Systems, Gregoriadis, Ed., Ch 2, (1980). However, available data indicated that the vesicles were unstable in vivo and that the radiolalel may have leaked, thus apparently prompting alternative theories such as prolonged circulation of vesicles and the release of drugs from such vesicles at a slower rate, and interaction of the liposomes with the capillary walls without actually crossing the wall surface, which presumably resulted in the drugs being detected within tumors. Id. Other researchers simply have concluded that the vesicles do not penetrate vascular walls after intravenous administration. B. Ryman et al., Biol. Cell, Vol. 47, pp. 71-80 (.983); G. Poste, Biol. Cell, Vol. 47, pp. 19-38 (1983).
Thus, although the prior art has recognized the necessity that vesicles carrying therapeutic drugs must cross vascular barriers to reach tumor cells, the experience of the art has taught that intravenous administration of micellular particles such as phospholipid vesicles is not effective to deliver encapsulated drugs to extravascular tumor cells.
This invention provides simple methods of enhancing extravasation of encapsulated chemotherapeutic agents to tumor cells within a body. The method of this invention further provides for the identification of such tumor sites in the body. This invention also provides for the delivery of chemotherapeutic agents to the cells of such tumors to combat such tumors.